And who of you by being worried can add a single hour to his life: tis de ex humon merimnon (PAPMSN) dunatai (3SPPI) prostheinai (AAN) epi ten helikian autou pecheun ena?: (Mt 5:36; Psalms 39:6; Ecclesiastes 3:14; Luke 12:25,26; 1 Corinthians 12:18)

able to add to his age one cubit? (Young's Literal)

See related resources...

How To Handle Fear Part 1
How To Handle Fear Part 2
How To Handle Fear Part 3
How To Handle Fear Part 4

1 Peter 5:7 Notes on casting your anxiety

What are we to do when we are worried?

Philippians 4:6 Notes on be anxious for nothing
Philippians 4:7 Notes on the peace of God

Being worried (3309) (merimnao from merimna  from merizo = divide - draw different directions ~ distraction) (Click word studies on merimnao and merimna) (Click in depth word study of Anxiety= merimna). Being worried is in the present tense which describes worry or anxiety as the habit of ones' life -- a veritable lifestyle of worry.

Add a single hour - We cannot add neither hour nor hair for earlier Jesus said...

you cannot make one hair white or black.

Add (4369) (prostithemi from prós = to or besides + títhemi = put) means to add something to an existing quantity. The Greek phrase may refer to adding time to one’s lifespan or to one's stature (height).

The question we need to ask is "Will worrying accomplish anything positive whatsoever?" In fact instead of adding "a single hour" worry tends to distract and breeds a loss of focus which results in loss of potentially productive time, not to mention the potentially damaging effects on one's health and longevity.

Hour (4083) (pechus) "cubit" is the length of a man's forearm from the inside of the elbow to the end of the longest finger.  Worry about the future is futile and a dishonor to God because it is an issue of not trusting in His sovereignty or total control.

No one can add an hour or an inch to life by worrying. In fact, worry does the opposite, reducing our life span and robbing us of joy. We must remember that our attitude is our choice.

Life (2244) (helikia from helix = adult, full–aged) refers to maturity of life in terms of either stature or size.

Jesus is saying in essence "Who by worrying can add an inch to his height or a single moment to his life?" The answer of course is no one can. This is the paradox about worry. In a manner of speaking, a man can "worry himself to death", but he cannot worry himself into a longer life! The writer of Hebrews says that...

And inasmuch as it is appointed for men to die once and after this comes judgment (see note Hebrews 9:27)

That is one appointment every person must keep and which cannot be postponed or rescheduled. Ray Pritchard illustrates with a humorous tale of two baseball players, George and John, writing that...

One day they were talking and John said, "Do you think they play baseball in heaven?" "I don't know," said George, "But if I get there before you do, I'll try to come back and let you know." Well, the very next week George died suddenly. A few days later John was out walking by himself when he heard a voice call his name. He looked around but no one was there. The voice called his name again. "Is that you, George?" he whispered. "Yes, it's me," said the voice. "Well, do they play baseball up there?" The voice answered, "John, I've got some good news and some bad news about that. The good news is, they play baseball up here all the time. The bad news is, they've got you scheduled to pitch next week." That's the way life is. One day you're shoveling snow; the next day you're pitching for the Angels. But it could happen to any of us...Nothing you can do can change that fact in the least. The whole matter is in God's hands. So to worry about terminal illness or a freak accident is pointless. Nothing you can do makes the slightest difference. You cannot by worrying add a single second to your life.

That lifts a tremendous load off your shoulders, doesn't it? You're going to die someday. Maybe today. Maybe tomorrow. Maybe later this year. But maybe not for fifty years. Maybe suddenly. Maybe slowly. Only God knows how it will happen. But that means you are living on borrowed time. Only God knows when your time is up and your appointment has come. That means you don't have to worry about dying. That's out of your hands. Therefore, you are free to relax, enjoy life, live each day to the fullest and go for all the gusto you can get. And let God worry about how things turn out. (Matthew 6:25-34 Three Things Not To Worry About)

And why are you worried about clothing?: kai peri endumatos ti merimnate? (2PPAI): (Mt 6:25,31; 10:10; Luke 3:11; 22:35,36)

Worried (3309) (merimnao from merimna  from merizo = divide - draw different directions - which is exactly what anxiety does to most of us!) (Click word studies on merimnao and merimna) expresses a strong feeling for something or someone, often to the point of being burdened. Although this can be a "positive" concern, in most of the NT uses it refers to an anxious concern, based on apprehension about possible danger or misfortune, and so it means to be worried about, to be anxious about, to be apprehensive (viewing the future with anxiety or alarm), to be unduly concerned, to be burdened with anxious care or cumbered with many cares and in simple terms to worry. The idea inherent in merimnao is of attempting to carry the burden of the future oneself and of unreasonable anxiety especially about things over which one has no control.

Worry has a fascinating etymology which can be traced back to the Old High German "wurgen" which means "to strangle" which is what worry does to our joy! Webster adds that in "dialect British" worry means to "choke" or to "strangle".  The first definition of "worry" in Webster is

"to harass by tearing, biting, or snapping especially at the throat", and then "to subject to persistent or nagging attention or effort" and "to afflict with mental distress or agitation = make anxious". (Merriam-Webster's Collegiate Dictionary. 10th ed. Springfield, Mass)

What a tragic state - a lifestyle characterized by constant worry! And yet don't many believers live in such a state? Jesus gives us the antidote to such mental "angst". Perhaps you need to memorize this section of Scripture so that you can recall Jesus' words to mind the next time those fiery missiles of worry and anxiety attack. That's when you need to take up the shield of faith to buttress yourself from those distractive, destructive thoughts.

But what does it mean in this context to take up the shield of faith? Biblical faith is not based on mental gymnastics but upon truth, specifically the truth of God's Word. And what is the truth that the God Man prescribes to counter the poison of worry? Obviously these passages are part of the answer. And yet do we really believe Jesus' Words? Do we take the necessary time to really study (see "observe" below) His Words? Faith comes by hearing and hearing by the Word of Christ. If we want to be fortified against the attacks of anxious thoughts, we must obey Jesus' command to closely and thoroughly study this section of Scripture. And given the tendency for all of us to forget what we once learned, we need to make a regular habit of coming back to this section, pondering it, praying through it, laying hold of it by faith, as if our very life depended on it, because in one sense it does! Man does not live by bread alone, but by every Word which proceeds from the mouth of God. We can know these truths intellectually, but Jesus wants us to know them intimately and internally... in our heart, in the control center of our very being. It is not God's will for His precious children to be fretting and worrying. Anxiety and worry is unavoidable because we live in a fallen world and even as redeemed believers still possess the old sin nature inherited from Adam. And so we are vulnerable to worry and anxiety, but we don't have to live in this condition continually if we heed Jesus' command.

Three times the sweet Psalmist David tells (commands) us not to fret (worry)...

(A Psalm of David.) Do not fret because of evildoers. Be not envious toward wrongdoers. (Why not?)
2 For they will wither quickly like the grass, and fade like the green herb.
3 Trust (a command, not a suggestion) in the LORD, and do (another command - faith that truly believes will behave) good; Dwell (command) in the land and cultivate faithfulness (What does "cultivate" picture? Is this not the time and effort you would invest in a newly planted, expensive fruit tree in your backyard. This is working out your salvation is fear and trembling knowing that you are not alone in the process, for it is God Who is at work in you, giving you the desire to obey Him and the power to do what pleases Him! - see notes Philippians 2:12; 13)
4 Delight (command) yourself in the LORD (Why? What is the advantage?) and He will give you the desires of your heart.
5 Commit (command)  your way to the LORD, Trust (command) also in Him, and He will do it.
6 And He will bring forth your righteousness as the light, and your judgment as the noonday.
7 Rest (command) in the LORD and wait (command) patiently for Him; Do not fret because of him who prospers in his way, because of the man who carries out wicked schemes.
8 Cease (command) from anger, and forsake (command) wrath; Do not fret, (Why not?) it leads only to evildoing. (You might want to read that again! Notice in verse 1 we are not to fret because of evil doers and here for the third time David [who well knew about "evil doers" such as Saul who desired to kill him!] warns us of the effects on us -- we are led to do evil!)

Spurgeon has these words on Psalm 37...

(Notes on verse 1) It is alas! too common for believers in their hours of adversity to think themselves harshly dealt with when they see persons utterly destitute of religion and honesty, rejoicing in abundant prosperity. Much needed is the command, Fret not thyself because of evildoers. To fret is to worry, to have the heartburn, to fume, to become vexed. Nature is very apt to kindle a fire of jealousy when it sees lawbreakers riding on horses, and obedient subjects walking in the mire: it is a lesson learned only in the school of grace, when one comes to view the most paradoxical providences with the devout complacency of one who is sure that the Lord is righteous in all His acts. It seems hard to carnal judgments that the best meat should go to the dogs, while loving children pine for want of it.

Neither be thou envious against the workers of iniquity. The same advice under another shape. When one is poor, despised, and in deep trial, our old Adam naturally becomes envious of the rich and great; and when we are conscious that we have been more righteous than they, the devil is sure to be at hand with blasphemous reasonings (Ed note: "fiery missiles"). Stormy weather may curdle even the cream of humanity. Evil men instead of being envied, are to be viewed with horror and aversion; yet their loaded tables, and gilded trappings, are too apt to fascinate our poor half opened eyes. Who envies the fat bullock the ribbons and garlands which decorate him as he is led to the shambles? Yet the case is a parallel one; for ungodly rich men are but as beasts fattened for the slaughter.

(Notes on verse 7) Rest in the Lord. This fifth is a most divine precept, and requires much grace to carry it out. To hush the spirit, to be silent before the Lord, to wait in holy patience the time for clearing up the difficulties of Providence -- that is what every gracious heart should aim at. "Aaron held his peace:" "I opened not my mouth, because thou didst it." A silent tongue in many cases not only shows a wise head, but a holy heart. And wait patiently for him. Time is nothing to him; let it be nothing to thee. God is worth waiting for. "He never is before his time, he never is too late." In a story we wait for the end to clear up the plot; we ought not to prejudge the great drama of life, but stay till the closing scene, and see to what a finis the whole arrives.

Fret not thyself because of him who prospereth in his way, because of the man who bringeth wicked devices to pass. There is no good, but much evil, in worrying your heart about the present success of graceless plotters: be not enticed into premature judgments -- they dishonour God, they weary yourself. Determine, let the wicked succeed as they may, that you will treat the matter with indifference, and never allow a question to be raised as to the righteousness and goodness of the Lord. What if wicked devices succeed and your own plans are defeated! there is more of the love of God in your defeats than in the successes of the wicked

(Notes on verse 8)  Cease from anger and forsake wrath. Especially anger against the arrangements of Providence, and jealousies of the temporary pleasures of those who are so soon to be banished from all comfort. Anger anywhere is madness, here it is aggravate insanity. Yet since anger will try to keep us company, we must resolvedly forsake it. Fret not thyself in any wise to do evil. By no reasonings and under no circumstances be led into such a course. Fretfulness lies upon the verge of great sin. Many who have indulged a murmuring disposition have at last come to sin, in order to gain their fancied rights. Beware of carping at others, study to be yourself found in the right way; and as you would dread outward sin, tremble at inward repining.  (See all of Spurgeon's notes on Psalm 37 - click here)

Clothing - Why does Jesus mention food and clothing? Aren't these the basic necessities of life? And as such these basic elements stand for all of the things we need to live in this world, including housing, jobs, money, etc. Jesus is saying don't worry about any of these things.

Observe how the lilies of the field grow; they do not toil nor do they spin:  katamathete (2PAAM) ta krina tou agrou pos auxanousin; ou kopiosin (3PPAI) oude nethousin: (Luke 12:27)

Observe (2648) (katamanthano from kata = prefix to intensify the meaning + manthano = intentional learning by inquiry & observation, genuinely understand and accept a teaching accept it as true and to apply it in one’s life) means to learn thoroughly, to study carefully so that one learns thoroughly.

Jesus is giving the antidote for worry or anxiety as a command not a suggestion --  Observe, study (aorist imperative = do this now, do it effectively, don't delay) the lilies well that may well learn thoroughly the lesson they teach.

Have you ever seen a worried lily? Do they toil and spin? Of course not. They don't have to because God takes care of them. But children of God are living souls of infinitely more value than the lilies of the field, for they have been redeemed by the precious blood of the Lamb. God will make sure your body is clothed with what you need.